jeffp1167

After replacing my 1990's thermostat the car ran great then all of a sudden started the climbing to 240 degrees before the thermostat opens. I know this is NOT an electrical issue with the cluster since I used a mechanical temp gauge to verify this was what the car was truly doin.

I am unsure of the brand of thermostat I used but the one I replaced with this new one did the exact same thing up until it just stopped opening.

So what is the ABSOLUTE best and most reliable thermostat out there ??????

another question .... I like the pressure relief radiator caps .... Can anyone tell me why they wont relieve pressure on a vette with the surge tank? I tested this cap on the radiator on my trans am and it worked fine however it will never vent into the coolant overflow jug no matter what.

pologreen1

I have never noticed a difference.

Aardwolf

I think you answered your own question with the pressure release not working. That is an air pocket causing both problems. Try burping it.

It's unlikely both 'stats are bad, though I've seen some fail. I like the balanced type thermostats like the one in the below. They fail less and are more accurate plus flow better and have a built in hole for bypass flow.

BADDUCK

It's probably an air pocket. If you want to check the thermostat you can do it with a pan of water and thermometer on the stove.

jeffp1167

when I replaced my head gaskets I opened the lower radiator petcock valve. After I put the motor back together I filled the block through the thermostat hole and it took a total of 3 - 3 1/2 gallons to fill everything up. does this sound right?

how do I work this air pocket out if thats what is the problem?

LT1CORVETTE

Yes, 3.5 gallons through the water pump thermostat sounds right.

The best way to avoid air pockets is to have everything together, open all bleed valves, slowly filling with coolant/h20 through the surge tank. Massage both radiator hoses (especially the lower while you are filling the car. Once coolant starts coming out of one of the bleed valves close it. Continue filling until the surge tank is full and then turn the car on, run for a few minutes and fill as necessary. Put the surge tank cap on, fill the over flow to full. Let the car get up to full temp then turn off and let it completely cool down. It will displace air in the system and draw more coolant in from the overflow tank. Continue the process over the next few days of getting the car up to full temperate and letting it completely cool down and make sure to keep topping off the overflow tank to the cool setting as necessary.

I have known people to run into problems refilling without having the bleed valves open or not massaging the coolant lines while refilling the system. It's a process on these cars, but the self bleeding of the system very efficient.

jeffp1167

what bleed valves?

theadmiral94

It does not sound like you have an 'air pocket' (I am assuming the car ran fine for more than just 1 or 2 days).

There may not be an 'absolute' best thermostat, as unfortunately, nothing in life is 'absolute'. However, given that you always 'get what you pay for', if your buying your thermostat at one of those 'chain' parts store, that could be your problem.

I've replaced thermostat's in 2 Vettes and 1 Pontiac TransAm over the past couple of years and have used OEM AC/Delco Thermostats WITHOUT any problems (from either National Parts Supply or the Dealer).

Regarding your cap problem, if you are also not hearing any pressure/bubbling in the overflow tank (up by the bumper), then perhaps the line between the black pressure tank and the overflow tank is clogged. Try removing the rubber line (upper hose) from the black pressure tank and applying a bit of air pressure (compressor, tire pumper, vacume blower) to the line to see if it will clear the line.

samsonb

I like the idea of the Robertshaw stat. But I've read alot and alot where they seem to fail way too often. And of people getting them where they test them, and they don't open at the right temp.

I'm thinking of just going with an AC Delco one. Though on those "Fail Safe" stats, I do wonder at what temp the "Fail Safe" kicks in? As I wonder if our cars run hotter than the manufacture takes into account when they design these?

GREGGPENN

The one I found matching the pic above is a Milodone brand.

samsonb

Actually, they are Robertshaw rebranded.

whalepirot

A $6 Robert Shaw 180 fixed the overheating issue with my 'hot' 406, after paying a boatload more for new water pump, new radiator, but before the professionally-suggested new fan.

samsonb

I was thinking of getting a Robertshaw stat, but I hear alot of complaints. As far as them falling apart out of the box. Not opening at the right time in boiling water. Etc. But the number one complaint I hear is them either getting stuck open or stuck closed alot.

I remember a few people going through 2-3 in a few months time. I'm thinking of just going with a Super Stant and drilling a 1/8" hole in it. Though Stant does make a stat has a jiggle valve in it. Where as it will let air bubbles pass through, ala drilled hole.

Though, on those Superstat, it talks about a V design of letting coolant slowly pass, and as it heats up, more of the coolant passes, then the stat eventually openings. Something about keep cold water from hitting a hot engine.